Stem cells refer to cells having not only self-replicating ability but also the ability to differentiate into at least two types of cells, and can be divided into totipotent stem cells, pluripotent stem cells, and multipotent stem cells.
Adult stem cells are obtained by taking cells from various human organs and developing the cells into stem cells and are characterized in that they differentiate into only specific tissues. However, recently, experiments for differentiating adult stem cells into various tissues, including liver cells, were dramatically successful, which comes into spotlight.
Multipotent stem cells were first isolated from adult bone marrow (Y. Jiang et al., Nature, 418:41, 2002), and then also found in other several adult tissues (C. M. Verfaillie, Trends Cell Biol., 12:502, 2002). In other words, bone marrow is the most widely known source of stem cells, multipotent stem cells were also found in the skin, blood vessels, muscles, and brain (J. G. Toma et al., Nat. Cell Biol., 3:778, 2001; M. Sampaolesi et al., Science, 301:487, 2003; Y. Jiang et al., Exp. Hematol., 30:896, 2002). However, stem cells are very rarely present in adult tissue such as bone marrow, and such cells are difficult to culture without inducing differentiation, and thus difficult to culture in the absence of specifically screened media. Namely, it is very difficult to maintain the isolated stem cells in vitro. Meanwhile, the results of studies on the isolation of mesenchymal stem cells from fetal tissue revealed that there are abundant mesenchymal stein cells in fetal tissue. However, the use of fetal tissue as the source of cell therapeutic agents has been limited due to ethical concerns. Mesenchymal stem cells were also isolated from umbilical cord blood (UCB) as the source of fetal mesenchymal stem cells (MSCs), but numbers were very small, and they showed poor proliferation.
In recent years, it was known that mesenchymal stem cells are present in the amnion (amniotic membrane or amniotic lining membrane), i.e., the thin innermost membrane sag surrounding the placenta and a developing mammalian embryo. Thus, technologies for isolating and culturing such mesenchymal stem cells have been developed (PCT International Patent Publication No. WO 2006/019357, Korean Patent Registration Nos. 0795708 and 0818214).
However, conventional methods for culturing amnion-derived stem cells have a shortcoming in that the time taken for stem cells to proliferate is long.
Accordingly, the present inventors have made extensive efforts to develop a method capable of increasing the proliferation rate of amnion-derived stem cells while maintaining the ability to differentiate, and as a result, have found that, when amnion-derived stem cells are cultured in a medium containing DMEM-P and KSFM-P, the ability of the cells to proliferate can be increased while maintaining the ability to differentiate, thereby completing the present invention.